Assessing the relative importance of earthworms as granivores under field conditions

Abstract

Plant communities are often seed-limited, and while rodents and birds are considered to be the primary contributors to surface seed removal, there is growing appreciation for the role of soil invertebrates, including earthworms. There have been very few studies assessing the relative importance of earthworms as granivores under field conditions compared to other taxa. We conducted a small-scale experiment in which we used earthworm inoculations and field exclosures to control access to surface-sown grass seed in an open field habitat and monitored impacts on initial grass recruitment. In isolation, earthworms reduced grass recruitment under field conditions (−22% biomass), but their impact was smaller than the reductions that occurred irrespective of earthworm presence when aboveground taxa had access to plots (−80–83%). The results of this small-scale study suggest that although earthworm-seed interactions may be ecologically important overall, in some habitats other taxa may be more influential than earthworms in terms of total surface seed removal.